1. Field of the Invention
The present invention relates to a method of detecting a fault of a frequency sensor and to a circuit implementing the method. More particularly, the circuit is for incorporating in a control device for controlling an aeroengine such as a turbojet.
2. Brief Discussion of the Related Art
Such a control device includes a computer that determines in particular the flow rate of fuel as a function of the temperature of the engine, of the speed of rotation of the high-pressure compressor, of the speed of rotation of the low-pressure compressor, of the pressures inside the engine, and of the states of various components of the engine. The speeds of rotation of the high-pressure compressor and of the low-pressure compressor are essential for controlling the engine and they are measured by frequency sensors such as phonic wheels, e.g. comprising a toothed wheel secured to the compressor shaft and surrounded by a coil.
In such an application, where a fault of the control device can have severe consequences for the operation of the aircraft, one of the main concerns is to detect faults and preferably to identify which components have failed.
At present, in the absence of such identification, the assembly comprising the sensor and the associated circuit is changed whenever a fault is detected. This gives rise to costs that are considerable.
Nevertheless, it is known to detect a lack of signal and to associate this state with a fault. The method is simple, effective, and enables open circuits and differential short circuits to be detected. However the method does not make it possible to detect short circuits to ground.
Such identification could also be implemented using complex electronic components. Unfortunately, the reliability of electronic components diminishes with increasing complexity, whereas their cost increases with increasing complexity.